The performance of a new biological water quality score system based on macroinvertebrates over a wide range of unpolluted running-water sites

Abstract

The occurrence of families of macroinvertebrates has recently been used as the basis for the BMWP (Biological Monitoring Working Party) system of assigning scores to lotic sites. In this study the performance of the system across 268 sites on 41 rivers providing a wide range of physical and chemical features has been appraised. Changes in score and ASPT (average score per taxon) with respect to season and sampling effort have been examined. Seasonal variations were relatively slight and it is concluded that samples taken in any of the three seasons, spring, summer or autumn, were likely to provide consistent estimates of score and particularly ASPT. Sample replication led to substantial accretion of scores but had little effect on ASPT and therefore more information was obtained for less effort when ASPT was used. Data are presented on score and ASPT values for 8 groups of sites derived by multivariate classificatory techniques. Considerable variability in achievable score and ASPT was observed in the different groups of unpolluted sites. In general, scores were highest in the group at the middle of the range of environmental features and lowest in groups at the bottom of the range (lowland areas). ASPT in contrast showed a relatively steady decline in values between groups at the top (mainly upland rivers) and bottom of the range of environmental features. Attempts were made to predict score and ASPT from physical and chemical data, or physical data alone using multiple regression. Equations used to predict ASPT explained on average a higher proportion of the variance (65%) than those predicting scores (22%). It is suggested that predictive equations for ASPT will enable theoretical ASPT to be calculated, thus providing target values against which observed values can be compared. Recommendations to facilitate use and interpretation of the BMWP score system are presented.